On Feb. 24, astronomers’ computers around the world lit up with a deluge of cosmic notifications — 800,000 alerts about new asteroids in our solar system, exploding stars across the galaxy and other noteworthy changes in the night sky. The discoveries were made by the Simonyi Survey Telescope at the in Chile and distributed globally within about two minutes.

That flurry of notifications marked the commencement of the observatory’s Alert Production Pipeline, a sophisticated software system developed at the 91̽�� that is eventually expected to produce up to seven million alerts per night.

“Rubin’s alert system was designed to allow anyone to identify interesting astronomical events with enough notice to rapidly obtain time-critical follow-up observations,” said , a research associate professor of astronomy at the 91̽��who leads the Alert Production Pipeline Group for the Rubin Observatory. “Rubin will survey the sky at an unprecedented scale and allow us to find the most rare and unusual objects in the universe. We can’t wait to see the exciting science that comes from these data.”

The beginning of scientific alerts is one of the last major milestones before Rubin Observatory launches its (LSST) later this year. During the LSST, Rubin will scan the Southern Hemisphere sky nightly for 10 years to precisely capture every visible change using . These alerts will chronicle the treasure trove of scientific discoveries that Rubin will make through its time-lapse record of the universe. In the first year of the LSST, Rubin is expected to capture images of more objects than all other optical observatories combined in human history.

The 91̽��played a central role in the software that enabled this month’s milestone. The alert pipeline was developed by a team of about two dozen researchers and software developers in the astronomy department’s . The team has spent the past decade working with other data management teams around the country to figure out how to process the staggering 10 terabytes of images that Rubin produces every night, and will continue to develop and operate the alert system throughout the 10-year LSST survey.

“Enabling real-time discovery on such a massive data stream has required years of technical innovation in image processing algorithms, databases and data orchestration. We’re thrilled to continue the UW’s legacy of excellence in data-driven science.” Bellm said.

While the night sky seems calm and unchanging to the casual viewer, it’s actually alive with motion and transformation. Each alert signals something that has changed in the sky since Rubin last looked — a new source of light, a star that brightened or dimmed, or an object that moved. With Rubin’s alerts, scientists will have a greater ability to catch supernovae in their earliest moments, discover and track asteroids to assess potential threats to Earth and spot rare interstellar objects as they race through the solar system.

Scientists can use these data to better understand the nature of dark matter, dark energy and other unknown aspects of the universe.

“The discoveries reported in these alerts reflect the power of NSF-DOE Rubin Observatory as a tool for astrophysics and the importance of sustained federal support,” said Kathy Turner, program manager in the High Energy Physics program in the U.S. Department of Energy’s . “Rubin Observatory’s groundbreaking capabilities are revealing untold astrophysical treasures and expanding scientists’ access to the ever-changing cosmos.”

Every 40 seconds during nighttime observations, Rubin captures a new region of the sky. It then sends the data on a seconds-long journey from Chile to the U.S. Data Facility (USDF) at the in California for initial processing. Rubin’s data management system automatically compares it to a template made from previous images of the same region. This comparison allows it to detect the slightest variations. With every change, such as the appearance of a new point of light, an object’s movement or a change in brightness, the system generates a public alert within two minutes.

“The scale and speed of the alerts are unprecedented,” says Hsin-Fang Chiang, a SLAC software developer leading operations for data processing at the USDF. “After generating hundreds of thousands of test alerts in the last few months, we are now able to say, within minutes, with each image, ‘Here is everything. Go.’”

Rubin’s alerts are public, meaning anyone — from professional researchers to students and citizen scientists — can access and explore them. The speed of the alerts allows scientists using other ground- and space-based telescopes around the world to coordinate follow-up observations. This collaboration will enable fast and detailed studies of unfolding phenomena.��

Additionally, through collaborations with platforms like , Rubin will empower the global community to help classify cosmic events and contribute directly to discovery.

Rubin Observatory is jointly operated by NSF and SLAC.

For more information, contact Bellm at ecbellm@uw.edu.

This story was adapted from a press release by and .

Operations of the Vera C. Rubin Observatory are funded by the U.S. National Science Foundation and the U.S. Department of Energy’s Office of Science.

UPDATE (January 27, 2026): This story has been updated to highlight the role of the Simonyi Survey Telescope in the research.

A team led by 91̽�� astronomers has discovered the fastest-ever spinning asteroid with a diameter over half a kilometer. The asteroid — found while analyzing data from the Simonyi Survey Telescope at the NSF–DOE Vera C. Rubin Observatory — is 0.4 miles in diameter and completes a full rotation every 1.88 minutes.

The study provides crucial information about asteroid composition and evolution. The discovery also demonstrates the potential of the observatory��as it prepares for a 10-year nightly survey of the Southern Hemisphere sky, the .

in Astrophysical Journal Letters.

“It’s really exciting that in some of the very first test images taken with the Vera C. Rubin Observatory that we’re already breaking records with the discovery of the fastest-spinning large asteroid found to date,” said lead author , a 91̽��affiliate assistant professor of astronomy and astronomer at . “With millions of new asteroids expected to be found by the Rubin Observatory in the near future, this is just the beginning of many exciting discoveries yet to come.”

The study uses data collected over the course of about 10 hours across seven nights in April and May 2025, during Rubin Observatory’s early commissioning phase. That same data revealed thousands of asteroids cruising about our solar system, about 1,900 of which have been confirmed as never-before-seen. Within that flurry, Greenstreet’s team at the 91̽��discovered 19 quickly rotating asteroids, including the record-breaking asteroid dubbed 2025 MN45.

As asteroids orbit the sun, they also rotate at a wide range of speeds. These spin rates not only offer clues about the conditions of their formation billions of years ago, but also tell us about their internal composition and evolution over their lifetimes. In particular, an asteroid spinning quickly may have been sped up by a past collision with another asteroid, suggesting that it could be a fragment of an originally larger object.

Fast rotation also requires an asteroid to have enough internal strength to not fly apart into many smaller pieces, called fragmentation. Most asteroids are “rubble piles,” which means they are made of many smaller pieces of rock held together by gravity, and thus have limits based on their densities as to how fast they can spin without breaking apart.��

“Clearly, this asteroid must be made of material that has very high strength in order to keep it in one piece as it spins so rapidly,” Greenstreet said. “We calculate that it would need a cohesive strength similar to that of solid rock, which is quite unusual.”��

Most fast rotators discovered so far orbit the sun just beyond Earth, known as near-Earth objects. Scientists find fewer fast-rotating main-belt asteroids, which orbit the sun between Mars and Jupiter, because their greater distance from Earth makes them fainter.

All but one of the newly identified fast-rotators, however, live in the main asteroid belt — an achievement made possible by Rubin’s enormous light-collecting power and precise measurement capabilities.

“As this study demonstrates, even in early commissioning, Rubin is successfully allowing us to study a population of relatively small, very rapidly rotating main-belt asteroids that hadn’t been reachable before,” Greenstreet said.

The discoveries of all 1,900 new asteroids, including the 19 fast rotators, were made possible by software developed by the UW . DiRAC’s software will power Rubin’s future solar system discoveries during its 10-year survey.

“These are exciting results but there’s much more to come,” said co-author Mario Jurić, a 91̽��professor of astronomy. “In the next two years, Rubin will discover a thousand times as many asteroids as were presented here. Rubin’s data will open the window into what’s out there in our solar system, and how it all came to be.”

91̽��co-authors include , a doctoral student in astronomy and astrobiology; , a postdoctoral researcher in astronomy; Devanshi Singh, an undergraduate student of physics and astronomy; , a professor of astronomy; , a software engineer in astronomy; , a research associate professor of astronomy; , a graduate student of astronomy; and , who worked on this study as research scientists in astronomy; , a research scientist in astronomy; and , a senior research scientist in astronomy. A full list of co-authors is .

This research was funded by the U.S. National Science Foundation and the U.S. Department of Energy. The DiRAC Institute is supported by the Charles and Lisa Simonyi Fund for Arts and Sciences, Janet and Lloyd Frink and the Washington Research Foundation.

For more information, contact Greenstreet at sarahjg@uw.edu.

This story was adapted from a press release by .

A new era of astronomy and astrophysics began Monday when the first images captured by the NSF–DOE were released, demonstrating the extraordinary capabilities of the new telescope and the world’s largest digital camera.

Officials in Washington, D.C., unveiled large, ultra-high-definition images and videos, as well as discoveries of thousands of new asteroids. Astronomers and researchers around the world watched along at viewing parties, including at the 91̽��’s Planetarium.

The images offer a preview of the most comprehensive census of the solar system scientists have ever conducted, and a peek into the exponential increase in discoveries and understanding of the cosmos this new telescope will make possible.

The 91̽��was one of the founding members of Rubin’s ambitious undertaking and will play a key role in making sense of the discoveries. 91̽��scientists and engineers were critical in advocating for the project, designing the observatory and developing the software that will analyze the petabytes of data from Rubin’s telescope, including the asteroid discovery algorithms.

“91̽�� faculty recognized early on that dreaming big about Rubin’s capabilities and leading the scientific charge would shape our knowledge of the solar system and propel innovation in data science not only in astrophysics but also across disciplines,” said 91̽��Provost Tricia R. Serio. “We often talk about the impact the 91̽��is making here and around the world. This project will take us far into space and give us information about the very origins of the universe and set the stage for future discoveries we can’t even imagine today.”

From its peak in the Chilean Andes, Rubin’s Simonyi Survey Telescope will scan the sky with its 8.4-meter mirror and enormous 3,200-megapixel camera, the largest digital camera in the world. The telescope’s sight path, the pace and frequency of observations and the vast field of vision required a new type of discovery algorithm to reliably make sense of the troves of data collected. Scientists and researchers at the 91̽��worked across disciplines to evolve data science and computer science to meet Rubin’s demands.

In 2017, the 91̽��— with founding support from the Charles and Lisa Simonyi Fund for Arts and Sciences — established the , or DiRAC. The Institute, part of the , aims to be an interdisciplinary hub to address fundamental questions about the origins and evolution of the universe. Leaders recognized that the future of astrophysics relied on using software as the chief instrument for this exploration. Combined with the UW’s and the deep connections to the Pacific Northwest’s tech community, DiRAC has developed a global reputation for working toward new discoveries.

As the Rubin sets out on a 10-year mission to conduct the Legacy Survey of Space and Time (LSST), software created at the 91̽��will be pivotal as scientists advance understanding of the cosmos and the origins of the solar system. UW’s faculty, students and staff have played key roles in the construction of this new facility They’ve also been pivotal in developing the algorithms that keep the telescope image sharp and creating the codes for mapping the solar system and discovering the most energetic and rarest phenomena in what astrophysicists call the ” UW’s , a professor of astronomy, is the director of the federally-funded Rubin Construction Project.��

Unlike other telescopes — which tend to focus and “zoom in” on a few objects of interest — Rubin is alone in the capability to quickly and repeatedly map the entire visible sky.��

“Rubin has the unprecedented capacity to capture the cosmos,” said , a professor of astronomy and director of UW’s . He’s also the co-principal investigator of the supported LSST Interdisciplinary Network for Collaboration and Computing (LINCC) Frameworks program to develop state-of-the-art analysis techniques capable of meeting Rubin’s scale and complexity.

“Rubin will deliver the largest map the universe ever made: tens of billions of galaxies, billions of stars and millions of new small bodies in our own solar system. It’s a data analysis endeavor of epic proportions,” Connolly said.��

For each object Rubin observes, there will be much more than a static image, the technology will produce a thousand-frame movie: trillions of measurements of billions of objects, said , a research associate professor and the science lead of Rubin’s time-domain software team.

“With these data, scientists will better understand the universe, chronicle its evolution, and delve into science ranging from dangerous asteroids to the mysteries of dark energy,” Bellm said.

For example, the UW’s team helped create simulation software to predict Rubin’s discoveries. The research found that the telescope will map more than 5 million main-belt asteroids, 127,000 near-Earth objects, 109,000 Trojan asteroids that share Jupiter’s orbit, 37,000 trans-Neptunian objects and about 2,000 Centaurs, or orbit-crossing objects.��

These objects, revealed in color and in more detail than was previously possible, help tell the story of the solar system’s origins, said , a professor of astronomy and the principal investigator of UW’s Rubin team.

Juric said that Rubin will help answer some fundamental questions: How did the planets form? Is there an unknown planet hiding in the outskirts of our solar system? Did comets bring water to the Earth? Or asteroids? And are there any that could still collide with us today?

“The first look we share today is a glimpse into the transformational capacity Rubin will bring to answer questions like these,” Juric said.

The work to support the Rubin Observatory hasn’t been limited to 91̽��faculty. Numerous 91̽��undergraduate and doctoral students have played contributing roles, authoring important journal articles, developing simulation software and writing complex computer codes.��

Exposure to the LSST has helped prepare students to succeed post graduation, whether applying for work in industry or moving onto advanced academic degrees.

“Developing cloud-based analytics platforms, or building pipelines to process large amounts of imaging data, are skills that allow one to do not just cutting-edge astronomy but also any other data-intensive problem,” said Steven Stetzler, who recently completed doctoral work at 91̽��and now holds a postdoctoral appointment at NASA’s Jet Propulsion Laboratory.

For more information, contact Juric at mjuric@uw.edu or James Davenport at jrad@uw.edu.��

A group of astronomers from across the globe, including a team from the 91̽�� and led by Queen’s University Belfast, have revealed new research showing that millions of new solar system objects will be detected by a brand-new facility, which is expected to come online later this year.����

The NSF–DOE is set to revolutionize our knowledge of the solar system’s “small bodies” — asteroids, comets and other minor planets.��

The Rubin Observatory, under construction on the Cerro Pachón ridge in northern Chile, features the 8.4-meter Simonyi Survey Telescope with a unique three-mirror design capable of surveying the entire visible sky every few nights. At its heart is the world’s largest digital camera — the 3.2 gigapixel Legacy Survey of Space and Time (LSST) Camera — covering a 9.6 square-degree field of view with six filters, roughly 45 times the area of the full moon. Together, this “wide-fast-deep” system will generate 20 terabytes of data every night — creating an unprecedented time-lapse “movie” of the cosmos over the next 10 years, and an incredibly powerful dataset with which to map the solar system.

The team of astronomers, led by Queen’s University’s , created , an innovative new open-source software used to predict what discoveries are likely to be made. Sorcha is the first end-to-end simulator that ingests Rubin’s planned observing schedule. It applies assumptions on how Rubin Observatory sees and detects astronomical sources in its images with the best model of what the solar system and its small body reservoirs look like today. ��

“Accurate simulation software like Sorcha is critical,” said Schwamb, a reader in the School of Mathematics and Physics at Queen’s University. “It tells us what Rubin will discover and lets us know how to interpret it. Our knowledge of what objects fill Earth’s solar system is about to expand exponentially and rapidly.”��

In addition to the eight major planets, the solar system is home to a vast population of small bodies that formed alongside the planets more than 4.5 billion years ago. Many of these smaller bodies remain essentially unchanged since the solar system’s birth, acting as a fossil record of its earliest days. By studying their orbits, sizes and compositions, astronomers can reconstruct how planets formed, migrated and evolved.

These objects — numbering in the tens of millions -— provide a powerful window into processes such as the delivery of water and organic material to Earth, the reshaping of planetary orbits by giant planets and the ongoing risk posed by those whose paths bring them near our planet.

In addition to Queen’s University and the UW, the international team includes researchers from the Center for Astrophysics | Harvard & Smithsonian and the University of Illinois Urbana-Champaign.��

A series of papers describing the software and the predictions have been accepted for publication by the Astronomical Journal and are .��

Beyond just finding these new small bodies, Rubin Observatory will observe them multiple times using different optical filters, revealing their surface colors. Past solar system surveys typically observed with a single filter.����

��“With the LSST catalog of solar system objects, our work shows that it will be like going from black-and-white television to brilliant color,” said , a doctoral student at Queen’s University. “It’s very exciting – we expect that millions of new solar system objects will be detected and most of these will be picked up in the first few years of sky survey.”��

The team’s simulations show that Rubin will map:��

• 127,000 near-Earth objects — asteroids and comets whose orbits cross or approach Earth. That’s more than tripling today’s known objects, about 38,000, and detecting more than 70% of potentially hazardous bodies larger than 140 meters. This will cut the risk of undetected asteroid impact of catastrophic proportions by at least two times, making a tremendous contribution to planetary defense.��
• Over 5 million main-belt asteroids, up from about 1.4 million, with precise color and rotation data on roughly one in three asteroids within the survey’s first years. This will give scientists unprecedented insight into the characteristics and history of the solar system’s building blocks.
• 109,000 Jupiter Trojans, bodies sharing Jupiter’s orbit at stable “Lagrange” points —�� more than seven times the number cataloged today. These bodies represent some of the most pristine material dating all the way back to the formation of the planets.��
• 37,000 trans-Neptunian objects, residents of the distant Kuiper Belt — nearly 10 times the current census — shedding light on Neptune’s past migration and the outer solar system’s history.��
• Approximately 1,500-2,000 , bodies on short-lived giant planet-crossing orbits in the middle solar system. Most Centaurs will eventually be ejected from the solar system, but a few lucky ones will survive to become short-period comets. The LSST will provide the first detailed view of the Centaurs and the important transition stage from Centaur to comet. �į��

Rubin Observatory’s LSST is a once-in-a-generation opportunity to fill in the missing pieces of our solar system, said , a member of the Sorcha team and a 91̽��professor of Astronomy. Juric also is a team lead of Rubin’s Solar System Processing Pipelines and a director of UW’s .��

“Our simulations predict that Rubin will expand known small-body populations by factors of 4–9x, delivering an unprecedented trove of orbits, colors and light curves,” Juric said. “With this data, we’ll be able to update the textbooks of solar system formation and vastly improve our ability to spot — and potentially deflect — the asteroids that could threaten Earth.”��

It took 225 years of astronomical observations to detect the first 1.5 million asteroids, and researchers found that Rubin will double that number in less than a year, said , a doctoral student at the UW.��

“Rubin’s unparalleled combination of breadth and depth make it a uniquely effective discovery machine,” Kurlander said.

, an assistant professor of Aerospace Engineering at the University of Illinois Urbana-Champaign added: “Only by debiasing LSST’s complex observing pattern can we turn raw detections into a true reflection of the solar system’s history — where the planets formed, and how they migrated over billions of years. Sorcha is a game changer in that respect.”

The Sorcha code is open-source and . By making these resources available, the Sorcha team has enabled researchers worldwide to refine their tools and be ready for the flood of LSST data that Rubin will generate, advancing the understanding of the small bodies that illuminate the solar system like never before.��

Rubin Observatory is event on June 23, offering the world an early glimpse of the survey’s power. Full science operations are slated to begin later this year.��

For more information, contact Juric at mjuric@uw.edu, Kurlander at jkurla@uw.edu, Schwamb at m.schwamb@qub.ac.uk, and Murtagh at jmurtagh05@qub.ac.uk.

Since 2018 the��, an international astronomical collaboration based at the Palomar Observatory in California, has scanned the entire sky every two to three nights. As part of this mission, the ZTF’s has been counting and cataloguing supernovae — flashes of light in the sky that are the telltale signs of stars dying in spectacular explosions.

On Dec. 4, ZTF researchers — including astronomers at the 91̽�� — announced that that they have identified more than 10,000 of these stellar events, the largest number ever identified by an astronomical survey.

“There are trillions of stars in the universe, and about every second, one of them explodes,” said Christoffer Fremling, an astronomer at Caltech who leads the Bright Transient Survey. “ZTF detects hundreds of these explosions per night and a handful are then confirmed as supernovae. Systematically doing this for seven years has led to the most complete record of confirmed supernovae to date.”

The Bright Transient Survey is currently the primary discovery pipeline for cosmic flashes — also known as astronomical transients — in the world. To determine which transients are supernovae, ZTF shares a stream of nightly transient detections with the wider astronomical community so that other telescopes around the world can conduct follow-up observations of candidate transients. This includes conducting a spectral analysis, in which instruments on observatory telescopes split the light from a transient object into its individual colors to reveal its distance from Earth and other properties.

“Classifying 10,000 supernovae is a tremendous achievement and will enable unprecedented scientific studies of explosive transients,” said ZTF team member , a 91̽��research associate professor of astronomy and scientist with the UW’s . “Reaching this milestone required careful technical work on scheduling and processing the ZTF discovery images, human and machine vetting of the alerts and obtaining timely follow-up spectra.”

For the Bright Transient Survey, a 60-megapixel wide-field camera mounted on Palomar’s Samuel Oschin telescope scanned the entire visible sky every two nights. To detect new astronomical events, astronomers subtracted images of the same portion of the sky from subsequent scans. Next, members of the ZTF team studied the subtracted images and triggered follow-up spectral observations by a second telescope at Palomar or other observatories.

Bellm, 91̽��research scientist and , 91̽��professor of astronomy and director of the DiRAC Institute, all contributed to the Bright Transient Survey. Bellm managed alerts of new transients and scheduled imaging for the survey. Jurić helped set up the ZTF’s automated system to alert team members around the world of new transients.

Developing automated analysis pipelines and alert systems are critical for the field as more powerful imaging technologies and new generations of observatories continue to transform astronomy into a “big data” endeavor. , a 20th century astronomer who first coined the term “supernova,” identified 120 supernovae in 52 years. The Bright Transient Survey by the ZTF — named for Zwicky — found 10,000 in a fraction of that time.

“The Bright Transient Survey program serves as an exemplar for the kinds of science we hope to do with the in the near future,” said Bellm.

Under construction in Chile, the Vera C. Rubin Observatory is the future home of the Legacy Survey of Space and Time, or LSST, a mission that will take deep images of the sky nightly and detect even more cosmic transients than ZTF. 91̽��scientists with the DiRAC Institute have been heavily involved in planning for the launch of the LSST. Collaborations like the ZTF have been a proving ground for developing and testing methods for use in the LSST.

For the Bright Transient Survey, Graham conducted follow-up spectral analyses of transients at in New Mexico. These efforts were especially valuable in catching some of the fainter, fading supernovae that would have been missed at Palomar.

“As 91̽��astronomers, we are so fortunate to have access to the Apache Point Observatory for our research,” said Graham. “One of the most impactful — and fun — parts of obtaining optical spectra is being surprised by rare transients with peculiar characteristics, which often reveal more about supernova physics than hundreds of ordinary objects. Figuring out how to do this work with the even larger number of LSST supernovae is the next big challenge.”

Most of the transients in the Bright Transient Survey are classified as one of two common types of supernovae: Type Ia, when a white dwarf steals so much material from another nearby star that it explodes, or Type II, when massive stars collapse and die under their own gravity. Thanks to the treasure trove of data from the Bright Transient Survey, astronomers are now better equipped to answer questions about how stars grow and die, as well as how dark energy drives the expansion of the universe.

After its expected 2025 commissioning, the Vera Rubin C. Observatory could discover millions more supernovae.

“The machine learning and AI tools we have developed for ZTF will become essential when the Vera Rubin Observatory begins operations,” said ZTF team member Daniel Perley, an astronomer at Liverpool John Moores University. “We have already planned to work closely with Rubin to transfer our machine learning knowledge and technology.”

With an additional $1.6 million of funding from the National Science Foundation, ZTF will continue to scan the night sky for the next two years.

“The period in 2025 and 2026 when ZTF and Vera Rubin can both operate in tandem is fantastic news for time-domain astronomers,” said Mansi Kasliwal, an astronomy professor at Caltech who will lead ZTF in the next two years. “Combining data from both observatories, astronomers can directly address the physics of why supernovae explode and discover fast and young transients that are inaccessible to ZTF or Rubin alone. I am excited about the future.”

For more information, contact Bellm at ecbellm@uw.edu and Graham at mlg3k@uw.edu.

Adapted from a by Caltech.

For decades, scientists have known that some galaxies reside in dense environments with lots of other galaxies nearby. Others drift through the cosmos essentially alone, with few or no other galaxies in their corner of the universe.

A new study has found a major difference between galaxies in these divergent settings: Galaxies with more neighbors tend to be larger than their counterparts, which have a similar shape and mass, but reside in less dense environments. In a published Aug. 14 in the Astrophysical Journal, researchers at the 91̽��, Yale University, the Leibniz Institute for Astrophysics Potsdam in Germany and Waseda University in Japan report that galaxies found in denser regions of the universe are as much as 25% larger than isolated galaxies.

The research, which used a new machine-learning tool to analyze millions of galaxies, helps resolve a long-standing debate among astrophysicists over the relationship between a galaxy’s size and its environment. The findings also raise new questions about how galaxies form and evolve over billions of years.

“Current theories of galaxy formation and evolution cannot adequately explain the finding that clustered galaxies are larger than their identical counterparts in less dense regions of the universe,” said lead author , a 91̽��postdoctoral researcher in astronomy and with the UW’s . “That’s one of the most interesting things about astrophysics. Sometimes what the theories predict we should find and what a survey actually finds are not in agreement, and so we go back and try to modify existing theories to better explain the observations.”

Past studies that looked into the relationship between galaxy size and environment came up with contradictory results. Some determined that galaxies in clusters were smaller than isolated galaxies. Others came to the opposite conclusion. The studies were generally much smaller in scope, based on observations of hundreds or thousands of galaxies.

In this new study, Ghosh and his colleagues utilized a survey of millions of galaxies conducted using the in Hawaii. This endeavor, known as the , took high-quality images of each galaxy. The team selected approximately 3 million galaxies with the highest-quality data and used a machine learning algorithm to determine the size of each one. Next, the researchers essentially placed a circle — one with a radius of 30 million light years — around each galaxy. The circle represents the galaxy’s immediate vicinity. They then asked a simple question: How many neighboring galaxies lie within that circle?

The answer showed a clear general trend: Galaxies with more neighbors were also on average larger.

There could be many reasons why. Perhaps densely clustered galaxies are simply larger when they first form, or are more likely to undergo efficient mergers with close neighbors. Perhaps dark matter — that mysterious substance that makes up most of the matter in the universe, yet cannot be detected directly by any current means – plays a role. After all, galaxies form within individual “halos” of dark matter and the gravitational pull from those halos plays a critical role in how galaxies evolve.

“Theoretical astrophysicists will have to perform more comprehensive studies using simulations to conclusively establish why galaxies with more neighbors tend to be larger,” said Ghosh. “For now, the best we can say is that we’re confident that this relationship between galaxy environment and galaxy size exists.”

Utilizing an incredibly large dataset like the Hyper Suprime-Cam Subaru Strategic Program helped the team reach a clear conclusion. But that’s only part of the story. The novel machine learning tool they used to help determine the size of each individual galaxy also accounted for inherent uncertainties in the measurements of galaxy size.

“One important lesson we had learned prior to this study is that settling this question doesn’t just require surveying large numbers of galaxies,” said Ghosh. “You also need careful statistical analysis. A part of that comes from machine learning tools that can accurately quantify the degree of uncertainty in our measurements of galaxy properties.”

The machine learning tool that they used is called GaMPEN — or Galaxy Morphology Posterior Estimation Network. As a doctoral student at Yale, Ghosh led development of GaMPEN, which was unveiled in papers published in and in the Astrophysical Journal. The tool is freely available online and could be adapted to analyze other large surveys, said Ghosh.

Though this new study focuses on galaxies, it also forecasts the types of research — centered on complex analyses of incredibly large datasets — that will soon take astronomy by storm. When a generation of new telescopes with powerful cameras, including the in Chile, come online, they will collect massive amounts of data on the cosmos every night. In anticipation, scientists have been developing new tools like GaMPEN that can utilize these large datasets to answer pressing questions in astrophysics.

“Very soon, large datasets will be the norm in astronomy,” said Ghosh. “This study is a perfect demonstration of what you can do with them — when you have the right tools.”

Co-authors on the study are , professor of physics and of astronomy at Yale; , a research fellow with the Leibniz Institute; , associate professor at Waseda University; , a Yale professor of astronomy; , professor of physics and of astronomy at Yale; , a doctoral student at Yale; and , professor of astronomy at the 91̽��and faculty member in the DiRAC Institute and the . The research was funded by NASA, the Yale Graduate School of Arts & Sciences, the John Templeton Foundation, the Charles and Lisa Simonyi Fund for Arts and Sciences, the Washington Research Foundation and the 91̽��eScience Institute.

For more information, contact Ghosh at aritrag@uw.edu.

Not all asteroids are alike. Some of them, known as “active” asteroids, sport comet-like tails of gas and dust. Studying active asteroids could reveal clues to how the solar system formed and how Earth became a water-bearing oasis for life. They may also aid future space missions.

Active asteroids are also rare. But now scientists have 15 new ones to study. They were spotted by , a partnership between NASA, the citizen science platform Zooniverse, astronomers and thousands of citizen scientist volunteers. The team announced its discoveries — among the first since the initiative was formed in 2021 — in a published March 15 in The Astronomical Journal.

“The collective effort of our volunteers has expanded our understanding of the solar system,” said project founder and lead author Colin Orion Chandler, a project scientist at the 91̽��’s . “The discoveries made by this diverse group of individuals highlight the importance of engaging the public in scientific endeavors.”

Around 8,300 volunteers combed through 430,000 images of known asteroids, looking for comet tails or other signatures of active asteroids. The images had been taken by the Victor M. Blanco Telescope at the in Chile. After searching for additional archival images of each candidate from the Active Asteroids project, the team discovered evidence of tails on more than a dozen objects. Some are in the Asteroid Belt, but others reside closer to Jupiter or wander the outer solar system.

“For an amateur astronomer like me it’s a dream come true,” said co-author Virgilio Gonano, an Active Asteroids volunteer in Udine, Italy. “Congratulations to all the staff and the friends that also check the images!”

Asteroids can become active due to impacts from other asteroids or by spinning so fast that they eject material off into space. Studying these objects is crucial for scientists to answer pressing questions about the formation and evolution of the solar system, including the origins of water here on Earth. Additionally, active asteroids may be valuable resources for future space exploration missions, because the same ices that are responsible for the comet-like tails could also be critical resources, such as the basis of rocket fuel or even breathable air.

Identifying active asteroids also helps scientists learn more about how often tail-generating events occur and help them understand asteroid behavior — insights that in turn can inform the design of future asteroid deflection endeavors like NASA’s recent .

“I have been a member of the Active Asteroids team since its first batch of data. And to say that this project has become a significant part of my life is an understatement,” said co-author Tiffany Shaw-Diaz, an Active Asteroids volunteer who lives in Dayton, Ohio. “I look forward to classifying subjects each day, as long as time or health permits, and I am beyond honored to work with such esteemed scientists on a regular basis.”

These efforts complement upcoming missions to rapidly identify solar system objects, such as the Legacy Survey of Space and Time based at the in Chile, which many 91̽��scientists are part of. And with its recent successes the Active Asteroids Citizen Science team will keep up the search for tails on asteroids near and far, including in the upcoming Rubin data, according to Chandler.

“This project not only furthers our knowledge of celestial bodies but also demonstrates the potential of citizen science in advancing cutting-edge research. Nine of the authors on this paper are citizen scientists,” said Chandler. “The success of this initiative reaffirms the importance of collaborative efforts in exploring the mysteries of the cosmos.”

Active Asteroids is accepting volunteers for its ongoing work:

The research was funded by NASA and the National Science Foundation.

For more information, contact Chandler at coc123@uw.edu.

Adapted from press releases by and .

A team of scientists has been tracking a bright object in the sky. But it’s not a star. It’s a new type of commercial satellite. Astronomers are trying to understand how its brightness and transmissions will interfere with Earth-based observations of the universe — and what can be done to minimize these effects as more of these satellites are launched.

In a published Oct. 2 in Nature, the team reports its first detailed assessment on how the satellite — — could impact astronomy.

“While there is only one BlueWalker 3 satellite, it is one of the brightest objects in the sky, and a harbinger of where low-Earth orbit is heading for sky observers,” said co-author , a research scientist with the 91̽��’s and the Vera C. Rubin Observatory in Chile.

Building on initial observations made shortly after its launch, these new results complement��of this unusual satellite. The paper includes details of how the satellite’s brightness changes over time, as well as the visibility of jettisoned hardware. With companies intending to deploy more commercial satellites in the coming years, this paper highlights the need for pre-launch impact assessments.

“The interference of satellites in astronomy has become an increasingly pressing issue over the last few years,”��said first author Sangeetha Nandakumar of the University of Atacama in Chile.

BlueWalker 3 was launched into low-Earth orbit on Sept. 10, 2022, by��. The craft is a prototype for a planned constellation of more than a hundred satellites for use in mobile communications. Observations made shortly after launch showed that the satellite was among the brightest objects in the sky.

To better understand its impact on astronomy, the International Astronomical Union’s , or CPS, initiated an international observing campaign. As part of this initiative, both professional and amateur observations were contributed from across the world from sites in Chile, the United States, Mexico, New Zealand, the Netherlands and Morocco.

“It is exciting that we could incorporate images from many different telescopes and visual observations from highly skilled amateur observers in this analysis,” said Rawls. “It’s an example of the kind of thing that is possible only when folks from many institutions and with many backgrounds work together with a common purpose.”

The CPS is co-hosted by NSF’s and the , an international partnership. The CPS facilitates global coordination of efforts by the astronomical community — in concert with observatories, space agencies, industry, regulators and other sectors — to help mitigate the negative consequences of satellite constellations on astronomy. Its four working groups — or hubs — pursue different projects analyzing different types of interference from satellites and other sources.

“This paper brings together observers from across the globe under the umbrella of the CPS SatHub to better understand the ramifications,” said Rawls, who co-leads SatHub. “This is the first peer-reviewed research to quantitatively measure the high brightness of BlueWalker 3 and discuss the impacts on astronomy.”

The newly released data show an abrupt increase in the brightness of BlueWalker 3 over a period of 130 days — coinciding with the complete unfolding of its antenna array — followed by fluctuations over the subsequent weeks. Data also showed a relationship between the varying brightness and other factors after unfolding, such as the satellite’s height above the horizon and the angle between the observer, the satellite and the sun. The team also used a subset of the observations to calculate the satellite’s trajectory over time. Comparing the predicted path with the observations collected, they could evaluate the accuracy of these predictions and observe how its elevation declined over time due to atmospheric drag and other factors.

In addition, they observed the launch vehicle adapter attached to BlueWalker 3 decoupling from the satellite. This component reached magnitude 5.5 in brightness, exceeding maximum recommendations set out by the IAU to avoid the worst impacts of satellites on optical astronomy.

“These results demonstrate a continuing trend towards larger, brighter commercial satellites, which is of particular concern given the plans to launch many more in the coming years,”��said co-author and CPS scientist Siegfried Eggl of the University of Illinois at Urbana-Champaign. “While these satellites can play a role in improving communications, it is imperative that their disruptions of scientific observations are minimized. This could preferably be achieved through continuing cooperation on mitigation efforts, or, if that is not successful, through a requirement for pre-launch impact assessments as part of future launching authorization processes.”

“Besides the effect on visible observations, BlueWalker 3 could also interfere with radio astronomy, since it transmits in radio frequencies close to those that radio telescopes observe in,”��said Federico Di Vruno, co-director of the CPS.��“The novel aspect of BlueWalker 3 is that it uses frequencies that are normally used by terrestrial transmitters.”

Observations of BlueWalker 3 will continue, with plans by astronomers to observe its thermal emission later this year. Astronomers will continue to discuss this topic at this month.

“This is a global issue, since satellites approved by any country are visible in the night sky across the world, highlighting the importance of international coordination,”��said co-author Jeremy Tregloan-Reed of the University of Atacama and the CPS.

For more information, contact Rawls at mrawls@uw.edu.

Adapted from a by the IAU.

An asteroid discovery algorithm — designed to uncover near-Earth asteroids for the ’s upcoming 10-year survey of the night sky — has identified its first “potentially hazardous” asteroid, a term for space rocks in Earth’s vicinity that scientists like to keep an eye on. The roughly 600-foot-long asteroid, designated , was discovered during a test drive of the algorithm with the survey in Hawaii. Finding 2022 SF289, which poses no risk to Earth for the foreseeable future, confirms that the next-generation algorithm, known as HelioLinc3D, can identify near-Earth asteroids with fewer and more dispersed observations than required by today’s methods.

“By demonstrating the real-world effectiveness of the software that Rubin will use to look for thousands of yet-unknown potentially hazardous asteroids, the discovery of 2022 SF289 makes us all safer,” said Rubin scientist , the principal developer of HelioLinc3D and a researcher at the 91̽��.

The solar system is home to tens of millions of rocky bodies ranging from small asteroids not larger than a few feet, to dwarf planets the size of our moon. These objects remain from an era over four billion years ago, when the planets in our system formed and took their present-day positions.

Most of these bodies are distant, but a number orbit close to the Earth, and are known as near-Earth objects, or NEOs. The closest of these — those with a trajectory that takes them within about 5 million miles of Earth’s orbit, or about 20 times the distance from Earth to the moon — warrant special attention. Such “potentially hazardous asteroids,” or PHAs, are systematically searched for and monitored to ensure they won’t collide with Earth, a potentially devastating event.

Scientists search for PHAs using specialized telescope systems like the NASA-funded ATLAS survey, run by a team at the University of Hawaii’s . They do so by taking images of parts of the sky at least four times every night. A discovery is made when they notice a point of light moving unambiguously in a straight line over the image series. Scientists have discovered about 2,350 PHAs using this method, but estimate that at least as many more await discovery.

From its peak in the Chilean Andes, the Vera C. Rubin Observatory is set to join the hunt for these objects in early 2025. Funded primarily by the U.S. National Science Foundation and the U.S. Department of Energy, Rubin’s observations will dramatically increase the discovery rate of PHAs. Rubin will scan the sky unprecedentedly quickly with its 8.4-meter mirror and massive 3,200-megapixel camera, visiting spots on the sky twice per night rather than the four times needed by present telescopes. But with this novel observing “cadence,” researchers need a new type of discovery algorithm to reliably spot space rocks.

Rubin’s solar system software team at the 91̽��’s has been working to just develop such codes. Working with Smithsonian senior astrophysicist and Harvard University lecturer , who in 2018 pioneered a new class of heliocentric asteroid search algorithms, Heinze and , a former 91̽�� researcher who is now an assistant professor at the University of Illinois at Urbana-Champaign, developed HelioLinc3D: a code that could find asteroids in Rubin’s dataset. With Rubin still under construction, Heinze and Eggl wanted to test HelioLinc3D to see if it could discover a new asteroid in existing data, one with too few observations to be discovered by today’s conventional algorithms.

and , lead ATLAS astronomers, offered their data for a test. The Rubin team set HelioLinc3D to search through this data and on July 18, 2023 it spotted its first PHA: 2022 SF289, initially imaged by ATLAS on September 19, 2022 at a distance of 13 million miles from Earth.

In retrospect, ATLAS had observed 2022 SF289 three times on four separate nights, but never the requisite four times on one night to be identified as a new NEO. But these are just the occasions where HelioLinc3D excels: It successfully combined fragments of data from all four nights and made the discovery.

“Any survey will have difficulty discovering objects like 2022 SF289 that are near its sensitivity limit, but HelioLinc3D shows that it is possible to recover these faint objects as long as they are visible over several nights,” said Denneau. “This in effect gives us a ‘bigger, better’ telescope.”

Other surveys had also missed 2022 SF289, because it was passing in front of the rich starfields of the Milky Way. But by now knowing where to look, additional observations from Pan-STARRS and Catalina Sky Survey quickly confirmed the discovery. The team used B612 Asteroid Institute’s to recover further unrecognized observations by the NSF-supported Zwicky Transient Facility telescope.

2022 SF289 is classified as an -type NEO. Its closest approach brings it within 140,000 miles of Earth’s orbit, closer than the moon. Its diameter of 600ft is large enough to be classified as “potentially hazardous.” But despite its proximity, projections indicate that it poses no danger of hitting Earth for the foreseeable future. Its discovery has been announced in the International Astronomical Union’s Minor Planet Electronic Circular .

Currently, scientists know of 2,350 PHAs but expect there are more than 3,000 yet to be found.

“This is just a small taste of what to expect with the Rubin Observatory in less than two years, when HelioLinc3D will be discovering an object like this every night,” said Rubin scientist Mario Jurić, director of the DiRAC Institute, professor of astronomy at the 91̽�� and leader of the team behind HelioLinc3D.�� “But more broadly, it’s a preview of the coming era of data-intensive astronomy. From HelioLinc3D to AI-assisted codes, the next decade of discovery will be a story of advancement in algorithms as much as in new, large, telescopes.”

Financial support for Rubin Observatory comes from the U.S. National Science Foundation, the U.S. Department of Energy and private funding raised by the LSST Corporation.

For more information, contact Heinze at aheinze@uw.edu and Jurić at mjuric@uw.edu.

By their own admission, and are interested in unusual stars. The 91̽�� astronomers were on the lookout for “stars behaving strangely” when an automated alert from the survey pointed them to Gaia17bpp. Survey data indicated that this star had gradually brightened over a 2 1/2-year period.

As Tzanidakis reported on Jan. 10 at the in Seattle, follow-up analyses indicated that Gaia17bpp itself wasn’t changing. Instead, the star is likely part of a rare type of binary system, and its apparent brightening was the end of a years-long eclipse by an unusual stellar companion.

“We believe that this star is part of an exceptionally rare type of binary system, between a large, puffy older star — Gaia17bpp — and a small companion star that is surrounded by an expansive disk of dusty material,” said Tzanidakis, a 91̽��doctoral student in astronomy. “Based on our analysis, these two stars orbit each other over an exceptionally long period of time — as much as 1,000 years. So, catching this bright star being eclipsed by its dusty companion is a once-in-a-lifetime opportunity.”

Since the Gaia spacecraft’s observations about the star only went back to 2014, Tzanidakis and Davenport, a 91̽��research assistant professor of astronomy and associate director of the , had to do a little detective work to reach this conclusion. First, they stitched together Gaia’s observations of the star with observations by other missions stretching back to 2010 — including , / and the .

Those observations, coupled with the Gaia data, showed that Gaia17bpp dimmed by about 4.5 magnitudes — or roughly 63 times. The star remained dim over the course of nearly seven years, from 2012 to 2019. The brightening that the Gaia survey had uncovered was the end of that seven-year dim.

No other stars near Gaia17bpp showed similar dimming behavior. Through the program, a digital catalog of more than a century’s worth of astro-photographic plates at Harvard, Tzanidakis and Davenport analyzed observations of the star stretching back to the 1950s.

“Over 66 years of observational history, we found no other signs of significant dimming in this star,” said Tzanidakis.

The two believe that Gaia17bpp is part of a rare type of binary star system, with a stellar companion that is — quite simply — dusty.

“Based on the data currently available, this star appears to have a slow-moving companion that is surrounded by a large disk of material,” said Tzanidakis. “If that material were in the solar system, it would extend from the sun to Earth’s orbit, or farther.”

During its eclipse, the unseen companion was blocking about 98% of Gaia17bpp’s light, according to Davenport.

A handful of other similar, “dusty” systems have been identified over the years, most notably Epsilon Aurigae, a star in the constellation Auriga that is eclipsed for two out of every 27 years by a relatively large, dim companion. The system that Tzanidakis and Davenport discovered is unique among these few dusty binaries in the length of the eclipse — at nearly seven years, it is by far the longest. Unlike the Epsilon Aurigae binary, Gaia17bpp and its companion are also so far apart that it would be centuries or more before an astute observer on Earth witnesses another such eclipse.

For Epsilon Aurigae and similar systems, the identity of the dusty companion is a matter of debate. Some preliminary data indicate that Gaia17bpp’s companion could be a small, massive white dwarf star. The source of its debris disk is also a mystery.

“This was a serendipitous discovery,” said Tzanidakis. “If we had been a few years off, we would’ve missed it. It also indicates that these types of binaries might be much more common. If so, we need to come up with theories about how this type of pairing even arose. It’s definitely an oddity, but it might be much more common than anyone has appreciated.”

Additional team members on this study are , a 91̽��research assistant professor of astronomy, and , a 91̽��graduate student in astronomy.

For more information, contact Tzanidakis at atzanida@uw.edu and Davenport at jrad@uw.edu.

NOTE: A previous version of this press release mis-reported the degree of dimming and brightening that Gaia17bpp underwent from 2012 to 2019.